Wind is being increasingly used as a source of energy for driving windmills or wind turbines, in order to generate electrical power. For example, large scale horizontal axis windmills have recently been used extensively to drive electrical generators. However, these devices suffer from several disadvantages, including noise concerns, danger to birds and air traffic, obscuring the landscape with banks of rotating windmills due to their large scale design, and in the case of large diameter horizontal axis propellers, having the propellers reach or exceed supersonic speeds at the tips of the rotors. Also, they are impractical for smaller, owner-controlled applications.
Vertical axis wind turbines are also known and typically have a central vertical rotor section having a series of vanes that serve to rotate the wind turbine around a central axle located on the wind turbine's vertical axis when wind, from any direction, impacts on the wind turbine. Therefore, while a horizontal axis windmill must turn to face the wind direction, the orientation of a vertical axis wind turbine (or “wind turbine”) remains unchanged regardless of wind direction. This reduces the design complexity of the wind turbine for use in smaller applications.
An early version of a vertical axis wind turbine was first disclosed by Savonius in U.S. Pat. No. 1,697,574, and later elaborated on in U.S. Pat. No. 1,766,765. These so-called “Savonius-type” vertical wind turbines provide a vertical axis wind turbine having at least two curved blades which overlap around an open central area in which area a central rotational axle was located. A substantially horizontal wind flow impacting on the Savonius-type vertical wind turbine causes an “S-shaped” flow of air through the centre of the wind turbine and thus causes the wind turbine to rotate. While the Savonius-type design provides the basis for a number of different wind turbine designs, it is common feature of these designs to have a vertical axle located in the center of the blades. However, this vertical axle creates unnecessary turbulence in the air flow through the wind turbine as the wind passes through the central opening between the blades.
Further, in some variations on this design, such as in U.S. Pat. No. 5,391,926 to Staley et al., or U.S. Pat. No. 5,852,331 to Giorgini, the blades of the wind turbine are, in fact, joined together at the centre axle so as to completely prevent wind from passing through the centre of the wind turbine.
Also, while Savonius states in U.S. Pat. No. 1,697,574 that various blade or vane designs such as cylindrical, helical, parabolical, conical, or spherical, might be used, the design provided in the patent is a merely a curved blade design which remains unchanged as one moves along the longitudinal axis of the wind turbine. No elaboration on the shapes or orientation of these alternative blade designs is provided. Further, while Giorgini also refers to a helical configuration, his design is better described as containing a curved rotor blade configuration.
As such, typical prior art Savonius-type, vertical wind turbines typically have a rotor blade design which is curved in the “x” and “y” axis, but is essentially linear in the “z” axis. That is, the blade position and shape are substantially unchanged as one moves along the vertical axis. Thus, a horizontal wind flow results in only a rotation force being applied to the wind turbine.
An additional issue in the design of any wind turbine is the need to reduce the rotation resistance, or in some cases, increase the rotation resistance, of the wind turbine rotor section. Typically, this rotation resistance is created by the weight of the turbine section of the wind turbine, as it rests on the base of the wind turbine. Commonly, in the Savonius-type design, this weight is supported, inter alia, by the centre axle which connects the turbine section to the base section, and thus, it would be beneficial to reduce the effective weight of the rotor section. However, in some applications, such as in conditions where high wind speeds are commonly encountered, such as on the tops of high buildings, it would be beneficial to increase the rotation resistance of the rotor section, as wind speeds increased. As such, it would be beneficial to provide a rotor section for a wind turbine which would either controllably reduce or increase its rotational resistance depending on its design parameters. Accordingly, providing a wind turbine in which the rotor section would provide either positive or negative lift would be of assistance in controlling the rotational resistance of the rotor section.
Also, it would be advantageous to provide a vertical axis wind turbine in which the turbulence in the centre of the rotor section of the wind turbine, caused by the centre axle, was effectively eliminated. It would also be advantageous to provide a wind turbine design in which the design of the wind turbine provided a reduction in the effective supported rotational weight of the turbine section of the wind turbine.